The field of the present invention is that of safety devices intended for locking a firing pin for a fuse of a spin-stabilised projectile.
Projectiles, notably medium caliber shells, are fitted with safety devices intended to prevent initiation of the pyrotechnic circuit before firing and during the first few tens of meters of their trajectory.
A known safety device includes a lock, for example, a split sleeve, which immobilises the projectile firing pin in translation, and which is surrounded by a spiral spring consisting of an elastic strip wound upon itself.
German Patent DE1197786 describes such a safety device for a medium caliber projectile fuse.
The lock includes a strip folded back upon itself so as to form a sleeve with a hexagonal profile. The sleeve acts as a stop for a shoulder on the firing pin thus preventing the pin from striking a detonator.
Because of its split structure, the lock is able to open under the action of the centrifugal force exerted upon it during firing. The opening of the lock allows the firing pin to move in translation, for example, at impact on a target.
A spiral spring is wound around the lock. The function of the spiral spring is to delay the time at which the lock opens. Since this opening occurs only after a few tens of meters of trajectory, the gun crew is protected.
The centrifugal force which acts on the spring during firing thus causes it progressively to unwind and to wind up against the wall of a cylindrical housing in the fuse. Once thee spring is completely unwound, the lock can then open and release the firing pin.
Such a device has disadvantages. For example misfires have been observed because the spring can form unwanted loops which interfere with the firing pin and prevent it from moving freely.